SAN FRANCISCO, California (Reuters) -- California Attorney General Bill Lockyer has filed a lawsuit to force top makers of potato chips and french fries to warn consumers about a potential cancer-causing chemical found in the popular snacks.

In a complaint filed Friday in Los Angeles Superior Court, Lockyer sought an injunction to stop restaurant chains such as McDonald's Corp. and Wendy's International Inc. from selling french fries without some form of warning.

Also named were producers of potato chips and other packaged potato products like PepsiCo's Frito-Lay Inc. and Procter & Gamble Co., makers of Pringles chips.

The suit asks manufacturers of these products to identify the dangers of high levels of acrylamide, a chemical that studies have found is created when starchy foods are cooked at high heat.

"I know from personal experience that, while these snacks may not be a necessary part of a healthy diet, they sure taste good," Lockyer said in a statement. "But I, and all consumers, should have the information we need to make informed decisions about the food we eat."

The lawsuit alleges that companies have violated a state law passed in 1986 requiring companies to provide warnings before exposing people to known carcinogens or reproductive toxins.

In 2002, scientists found potatoes and other starchy foods cooked at high temperatures contained low levels of acrylamide. Other studies have discounted the potential toxicity of acrylamide to humans.

Acrylamide study
The U.S. Food and Drug Administration is studying the impact of acrylamide levels in food. In a March press release, the FDA said "acrylamide can cause cancer in laboratory animals at high doses, although it is not clear whether it causes cancer in humans at the much lower levels found in food."

Acrylamide is also widely used for industrial purposes, including sewage treatment.

Other defendants named in the suit include Burger King Corp., KFC Corp., a unit of Yum Brands Inc., for its KFC Potato Wedges, Kettle Foods Inc., makers of Kettle chips, which bills itself as a natural health food brand, and Cape Cod Potato Chips Co. of Hyannis, Massachusetts, a unit of Lance Inc.

In June, a California consumer group pressed the attorney general's office to take this action. At that time, Frito-Lay issued a statement saying its "food safety standards are very stringent and meet all federal and state regulations."

Procter & Gamble spokeswoman Kay Puryear said company researchers have been investigating issues raised by the 2002 acrylamide study, she said.

"Acrylamide is available whether those foods are prepared in a restaurant, at home or by the packaged goods industry," she said. "We stand behind, and absolutely think, our products are as safe as ever."

Burger King spokeswoman Edna Johnson said she had not seen the suit because her company's Miami headquarters had been closed in the wake of Hurricane Katrina. "As a matter of company policy we don't comment on pending legal matters," she said.